Analog switches, such as transmission gates or transfer gates built using transistors, can be used to selectively pass or block analog signals. An ideal semiconductor based analog switch operates like a mechanical switch, for example like a light switch. In an ‘on’ state, the analog switch should pass a signal between its nodes like a short circuit. In an ‘off’ state the switch should act as an open circuit.
A problem associated with semiconductor based analog switches is that they can fail to operate like a mechanical switch. For example, the semiconductor based analog switch can sometimes end up partially on even when it should be ‘off’ or the analog switch can be slow to switch between ‘off’ and ‘on’. In order for the semiconductor based switches to operate more like mechanical switches often they need to operate with specified parameters. For example, the signal the analog switch is switching can be limited by the voltage range applied to the gate terminals of the transistors forming the switches. The gate terminal can be used to switch the transistor off and on, in this way it operates like a faucet valve controlling the flow of current between the source and drain terminals of the transistor. The voltage range that can be applied to the gate is usually limited to the voltage supply to available in the circuit, which is sometimes called a supply rail. When an input signal falls outside of the device's supply rails, i.e. exceeds the most positive supply voltage or falls below the most negative supply voltage, many analog switches exhibit non-ideal behavior, significant including leakage in the “off” state and decreased switching speed and linearity. This is undesirable.